Journal of the American Chemical Society, Vol.129, No.35, 10847-10857, 2007
Synthesis and characterization of the homologous m-m bonded series Ar' MMAr' (M = zn, cd, or hg; Ar' = C6H3-2,6-(C6H3-2,6-Pr'(2))(2)) and related arylmetal halides and hydride species
The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are reported. The compounds Ar'MMAr' (M = Zn, Cd, or Hg; Ar' = C6H3-2,6-(C6H3-2,6-Pr'(2))(2)) were synthesized by reduction of the corresponding arylmetal halides by alkali metal/ graphite (Zn or Hg) or sodium hydride (Ccl). These compounds possess almost linear C-M-M-C core structures with two-coordinate metals. The observed M-M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) A for the zinc, cadmium, and mercury species, respectively. The shorter Hg-Hg bond in comparison to that of Cd-Cd is consistent with DFT calculations which show that the strength of the Hg-Hg bond is greater. The arylimetal halides precursors (ArMI)(1 or 2), and the highly reactive hydrides (ArMH)(1 or 2), were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar'HgI, is monomeric. The arylzinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) Ar'-H-bridged structures. The Ar'HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar'HgH by Ar'H. It was also shown that the decomposition of Ar'Cd(mu-H)(2)CdAr' at room temperature leads to the M-M bonded ArCdCdAr', thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate.